OPERATION OF A QUADRUPOLE ION-TRAP FOR PARTICLE BEAM LC/MS ANALYSES

Several operational modes of the quadrupole ion trap mass spectrometer (QITMS) were investigated to perform particle beam (PB) LC/MS analyses. The PB interface was directly coupled to a QITMS without the use of an external ion source; vaporization of the particle beam and ionization by electron ionization (EI) were accomplished within the ion trap. Ions from residual LC solvent initially caused space charging and a significant extent of chemical ionization (CI), which degraded the quality of EI mass spectra. Ejection of solvent ions prior to mass analysis minimized both space charging and CI, which allowed acquisition of EI spectra that compared favorably to EI spectra obtained from pure samples vaporized off of a solids probe and to library EI spectra. Isocratic LC/PB/QITMS analyses for several pesticides show lower limits of detection (LODs) than those reported for LC/PB/MS analyses on PB systems using quadrupole mass analyzers. Typically nonlinear calibration curves are produced, although linear calibrations have been observed for some analytes.